There has been proposed a light emitting device which changes wavelength of a part of light from the light-emitting element by the fluorescent material, and mixes the light which has been subjected to wavelength conversion and the light from the light-emitting element, thereby enabling to emit a color different from an emission light color of the light-emitting element itself. For example, a light emitting device which has a structure where a light-emitting element for emitting blue light and a fluorescent material excited by the blue light to thereby emit light with wavelength larger than that of the blue light are combined has been known.
The above existing light emitting device uses the blue light, that is, light in a visible region as an excitation light of the fluorescent material. Herein, excitation efficiency or light-emitting efficiency of the fluorescent material varies according to the wavelength of the excitation light. In general, in the case of using the light in the visible region as the excitation light, the excitation efficiency is decreased. Accordingly, the above light emitting device is low in the excitation efficiency of the fluorescent material, and it cannot convert at high efficiency the wavelength of the light from the light-emitting element to radiate it outside. In addition, when the excitation efficiency of the fluorescent material is low, loss of the blue light of the light-emitting element is made large, and the quantity of the blue light which has not been subjected to wavelength conversion and radiated outside is made smaller. As seen in the conventional structure, not only the quantity of the light obtained by converting light from the light-emitting element in wavelength but the quantity of the light emitted from the light-emitting element and directly radiated outside is reduced. Consequently, total light output power (luminance) of the light emitting device decreases as a whole.
The invention has been made in view of the above problems. It is an object of the invention to provide a light emitting device which uses a single light source (light-emitting element) and can emit, at high efficiency, light of color different from an emission light color of the light-emitting element itself. In particular, the invention aims to provide a light emitting device which can emit, at high efficiency, white light or light with mixed color of lights of two or more wavelengths.